1. Field of the Invention
The present invention relates to a pressure-sensitive adhesive composition, and a pressure-sensitive adhesive layer and a pressure-sensitive adhesive sheet that have the pressure-sensitive adhesive composition.
2. Description of the Related Art
A pressure-sensitive adhesive sheet is used for adhering adherends to each other or for fixing an article to an adherend by being firmly adhered to the adherend. In this case, a pressure-sensitive adhesive tape having the following characteristics is required: the pressure-sensitive adhesive force of which, occurring at the beginning of attachment, is small, because it is difficult to reattach the tape if the tape has large pressure-sensitive adhesive force from the beginning of attachment; while the pressure-sensitive adhesive force of which is increased over time such that large pressure-sensitive adhesive force can be obtained, in terms of fixing members in home electrical appliances and mobile devices, etc.
In order to meet such a change in pressure-sensitive adhesive force, methods for changing the pressure-sensitive adhesive force of pressure-sensitive adhesive sheets by heating or ultraviolet irradiation have traditionally been used (see Patent Documents 1 to 3).
A pressure-sensitive adhesive sheet having the following properties is also required: when a pressure-sensitive adhesive sheet is peeled from an adherend, the adherend is hard to be contaminated or there is little adhesive deposit remaining on the adherend.
[Patent Document 1] Japanese Patent Application Publication No. 1999-302610
[Patent Document 2] Japanese Patent Application Publication No. 1999-302614
[Patent Document 3] Japanese Patent Application Publication No. 2011-127054
There has been the problem that the method for changing the pressure-sensitive adhesive force of a pressure-sensitive adhesive sheet by heating or ultraviolet irradiation cannot be applied to an adherend that may be adversely affected by these treatments. There is actually a method for reducing pressure-sensitive adhesive force by temporarily forming a layer having small cohesive force on the interface between a pressure-sensitive adhesive and an adherend with the use of an additive, etc.; in such a method, however, there occurs the problem that, after a pressure-sensitive adhesive sheet is peeled in the state where the pressure-sensitive adhesive force is small, the adherend may be contaminated by adhesive deposit or attached additives, which causes the adherend to be adversely affected or makes it difficult to reuse the adherend. Accordingly, in a traditional pressure-sensitive adhesive, reworkability to various adherends, which is obtained by small pressure-sensitive adhesive force occurring at the beginning of attachment, an increase in adhesiveness occurring over time, and a low contamination property have not been entirely achieved.